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.Dd August 9, 2019
.Dt ZPOOL-IOSTAT 8
.Os Linux
.Sh NAME
.Nm zpool Ns Pf - Cm iostat
.Nd Display logical I/O statistics for the given ZFS storage pools/vdevs
.Sh SYNOPSIS
.Nm
.Cm iostat
.Op Oo Oo Fl c Ar SCRIPT Oc Oo Fl lq Oc Oc Ns | Ns Fl rw
.Op Fl T Sy u Ns | Ns Sy d
.Op Fl ghHLnpPvy
.Oo Oo Ar pool Ns ... Oc Ns | Ns Oo Ar pool vdev Ns ... Oc Ns | Ns Oo Ar vdev Ns ... Oc Oc
.Op Ar interval Op Ar count
.Sh DESCRIPTION
.Bl -tag -width Ds
.It Xo
.Nm
.Cm iostat
.Op Oo Oo Fl c Ar SCRIPT Oc Oo Fl lq Oc Oc Ns | Ns Fl rw
.Op Fl T Sy u Ns | Ns Sy d
.Op Fl ghHLnpPvy
.Oo Oo Ar pool Ns ... Oc Ns | Ns Oo Ar pool vdev Ns ... Oc Ns | Ns Oo Ar vdev Ns ... Oc Oc
.Op Ar interval Op Ar count
.Xc
Displays logical I/O statistics for the given pools/vdevs. Physical I/Os may
be observed via
.Xr iostat 1 .
If writes are located nearby, they may be merged into a single
larger operation. Additional I/O may be generated depending on the level of
vdev redundancy.
To filter output, you may pass in a list of pools, a pool and list of vdevs
in that pool, or a list of any vdevs from any pool. If no items are specified,
statistics for every pool in the system are shown.
When given an
.Ar interval ,
the statistics are printed every
.Ar interval
seconds until ^C is pressed. If 
.Fl n
flag is specified the headers are displayed only once, otherwise they are 
displayed periodically. If count is specified, the command exits
after count reports are printed. The first report printed is always
the statistics since boot regardless of whether
.Ar interval
and
.Ar count
are passed. However, this behavior can be suppressed with the
.Fl y
flag. Also note that the units of
.Sy K ,
.Sy M ,
.Sy G ...
that are printed in the report are in base 1024. To get the raw
values, use the
.Fl p
flag.
.Bl -tag -width Ds
.It Fl c Op Ar SCRIPT1 Ns Oo , Ns Ar SCRIPT2 Oc Ns ...
Run a script (or scripts) on each vdev and include the output as a new column
in the
.Nm zpool Cm iostat
output. Users can run any script found in their
.Pa ~/.zpool.d
directory or from the system
.Pa /etc/zfs/zpool.d
directory. Script names containing the slash (/) character are not allowed.
The default search path can be overridden by setting the
ZPOOL_SCRIPTS_PATH environment variable. A privileged user can run
.Fl c
if they have the ZPOOL_SCRIPTS_AS_ROOT
environment variable set. If a script requires the use of a privileged
command, like
.Xr smartctl 8 ,
then it's recommended you allow the user access to it in
.Pa /etc/sudoers
or add the user to the
.Pa /etc/sudoers.d/zfs
file.
.Pp
If
.Fl c
is passed without a script name, it prints a list of all scripts.
.Fl c
also sets verbose mode
.No \&( Ns Fl v Ns No \&).
.Pp
Script output should be in the form of "name=value". The column name is
set to "name" and the value is set to "value". Multiple lines can be
used to output multiple columns. The first line of output not in the
"name=value" format is displayed without a column title, and no more
output after that is displayed. This can be useful for printing error
messages. Blank or NULL values are printed as a '-' to make output
awk-able.
.Pp
The following environment variables are set before running each script:
.Bl -tag -width "VDEV_PATH"
.It Sy VDEV_PATH
Full path to the vdev
.El
.Bl -tag -width "VDEV_UPATH"
.It Sy VDEV_UPATH
Underlying path to the vdev (/dev/sd*).  For use with device mapper,
multipath, or partitioned vdevs.
.El
.Bl -tag -width "VDEV_ENC_SYSFS_PATH"
.It Sy VDEV_ENC_SYSFS_PATH
The sysfs path to the enclosure for the vdev (if any).
.El
.It Fl T Sy u Ns | Ns Sy d
Display a time stamp.
Specify
.Sy u
for a printed representation of the internal representation of time.
See
.Xr time 2 .
Specify
.Sy d
for standard date format.
See
.Xr date 1 .
.It Fl g
Display vdev GUIDs instead of the normal device names. These GUIDs
can be used in place of device names for the zpool
detach/offline/remove/replace commands.
.It Fl H
Scripted mode. Do not display headers, and separate fields by a
single tab instead of arbitrary space.
.It Fl L
Display real paths for vdevs resolving all symbolic links. This can
be used to look up the current block device name regardless of the
.Pa /dev/disk/
path used to open it.
.It Fl n
Print headers only once when passed
.It Fl p
Display numbers in parsable (exact) values. Time values are in
nanoseconds.
.It Fl P
Display full paths for vdevs instead of only the last component of
the path. This can be used in conjunction with the
.Fl L
flag.
.It Fl r
Print request size histograms for the leaf vdev's IO. This includes
histograms of individual IOs (ind) and aggregate IOs (agg). These stats
can be useful for observing how well IO aggregation is working.  Note
that TRIM IOs may exceed 16M, but will be counted as 16M.
.It Fl v
Verbose statistics Reports usage statistics for individual vdevs within the
pool, in addition to the pool-wide statistics.
.It Fl y
Omit statistics since boot.
Normally the first line of output reports the statistics since boot.
This option suppresses that first line of output.
.Ar interval
.It Fl w
Display latency histograms:
.Pp
.Ar total_wait :
Total IO time (queuing + disk IO time).
.Ar disk_wait :
Disk IO time (time reading/writing the disk).
.Ar syncq_wait :
Amount of time IO spent in synchronous priority queues.  Does not include
disk time.
.Ar asyncq_wait :
Amount of time IO spent in asynchronous priority queues.  Does not include
disk time.
.Ar scrub :
Amount of time IO spent in scrub queue. Does not include disk time.
.It Fl l
Include average latency statistics:
.Pp
.Ar total_wait :
Average total IO time (queuing + disk IO time).
.Ar disk_wait :
Average disk IO time (time reading/writing the disk).
.Ar syncq_wait :
Average amount of time IO spent in synchronous priority queues. Does
not include disk time.
.Ar asyncq_wait :
Average amount of time IO spent in asynchronous priority queues.
Does not include disk time.
.Ar scrub :
Average queuing time in scrub queue. Does not include disk time.
.Ar trim :
Average queuing time in trim queue. Does not include disk time.
.It Fl q
Include active queue statistics. Each priority queue has both
pending (
.Ar pend )
and active (
.Ar activ )
IOs. Pending IOs are waiting to
be issued to the disk, and active IOs have been issued to disk and are
waiting for completion. These stats are broken out by priority queue:
.Pp
.Ar syncq_read/write :
Current number of entries in synchronous priority
queues.
.Ar asyncq_read/write :
Current number of entries in asynchronous priority queues.
.Ar scrubq_read :
Current number of entries in scrub queue.
.Ar trimq_write :
Current number of entries in trim queue.
.Pp
All queue statistics are instantaneous measurements of the number of
entries in the queues. If you specify an interval, the measurements
will be sampled from the end of the interval.
.El
.El
.Sh SEE ALSO
.Xr zpool-list 8 ,
.Xr zpool-status 8 ,
.Xr iostat 1 ,
.Xr smartctl 8
